512 Shove.—On the Structure of the 
exterior as to show an almost complete absence of paren¬ 
chymatous tissue. The roots in general originate at points 
where the steles anastomose ; this is so in the case of the 
roots shown in Fig. 5. 
Histological Structure. 
I. Stem. 
A transverse section of the stem of Angiopteris shows the 
vascular bundles grouped in roughly concentric circles ; the 
arrangement has been described and figured by Mettenius 1 . 
The outline of the stem-steles, as seen in transverse section, 
varies from roughly circular to strap-shaped, the latter 
arising by the union of two or more of the former. 
Union takes place between steles lying right and left of 
each other, and not between those lying approximately on 
the same radius, except in connexion with the giving off 
of leaf-trace bundles or compensating strands. The longer 
diameter of the strap-shaped steles varies from 15 to 3 mm.; 
the more or less circular steles measure from 5 to 2 mm. 
across. 
A transverse section of the stem at any level does not cut all 
the steles transversely, owing to the oblique direction of their 
course; hence, to determine the position of the protoxylem 
for a whole section, it is necessary to isolate each stele and 
to cut it separately. As a result of such procedure it was 
found that the steles are both mesarch and endarch in struc¬ 
ture. Fig. 2 shows the position of the protoxylem groups 
for a complete transverse section of the stem. The proto¬ 
xylem elements are recognized in the mature steles by their 
small size and frequently crushed condition; they appear 
thus in Figs. 21 and 2 6. 
The investigation of very young steles taken from the 
apical region of the stem confirms the results obtained from 
the consideration of the mature bundles. In these young 
Mettenius (’64), Taf. I, Fig. 1 . 
